U.S. Pat. No. 2,908,516 (Stein), issued on Oct. 13, 1959, discloses a shaft seal of the type described above. Sliding ring seals are generally used where the r.p.m. and peripheral speeds are high. Such sliding ring seals are used to maximally avoid the exchange of fluid or pressure equalization between two chambers partitioned by a machine casing through which the shaft extends. Sliding ring seals often have slots or grooves in their circumferential surface facing the shaft, said slot communicating with a fluid chamber of the casing. Due to the hydrodynamic action of the fluid between the shaft and sliding rings, these rings lift clear off the shaft thereby reducing the abrasive seal wear. Such sliding constructions have been disclosed, for example in German Patent Publication DE 2,646,475 B2 (Stein), published Dec. 15, 1977. However, to limit the leakage through the clearance between the shaft and the sliding ring, U.S. Pat. No. 2,908,516 (Stein) teaches using a tension spring around the casing facing the circumferential surface of the circumferentially segmented slide ring to urge the ring against the shaft.
However, it has been shown that such slide ring seals are no longer sufficient to ensure the necessary sealing integrity when circumferential speeds exceed about 30 m/s and a differential pressure between the two chambers to be sealed from each other exceeds 100 kPa.